Tes"ter, n. [For testern, teston, fr. F. teston, fr. OF. teste the head, the head of the king being impressed upon the coin. See Tester a covering, and cf. Testone, Testoon.]

An old French silver coin, originally of the value of about eighteen pence, subsequently reduced to ninepence, and later to sixpence, sterling. Hence, in modern English slang, a sixpence; -- often contracted to tizzy. Called also teston.